The present invention relates to a method and apparatus for killing flying insects by spraying insecticide into the air in which the insects are flying, and in particular to methods of improving the targeting of the insects with the insecticide.
The efficiency of insecticide sprays in killing flying insects depends, in part, upon how much of the insecticide contacts the insects which are to be killed. Current methods of applying the insecticide rely on the mechanical interaction between the sprayed droplets of insecticide and each flying insect. Aerosol insecticide sprays may be dispersed into areas through which insects may fly and thus encounter the droplets of insecticide, or aerosol insecticide sprays may be aimed at specific target insects. Due to the high density of insecticide droplets in the plume produced during spraying, there is a high probability that contact will occur between the insects and the droplets. However, when insects are in flight the air disturbances around their bodies caused by the beating of wings may actually push droplets away. The probability of a flying insect coming into contact with one or more aerosol insecticide droplets is thus largely determined by mechanical forces, whilst the probability of knock-down or kill is subsequently determined by the concentration and toxicity of the active ingredient in the insecticide being used.
Spraying apparatus for producing a spray of liquid droplets is well known. For example, such apparatus is known in the domestic environment for producing sprays of droplets of insecticides or polish or air freshening compositions. Generally, such apparatus includes a reservoir for accommodating the liquid composition to be sprayed, a spraying head including a bore through which the composition is expelled in the form of a spray of droplets, and a conduit system whereby the composition can pass from the reservoir to the spraying head. The apparatus may preferably be in the form of an aerosol in which case it includes gas under pressure, possibly in a liquid state, which expels the liquid composition (to be sprayed) from the reservoir to the spraying head and then out of the spraying head in the form of a spray of droplets.
Generally, the droplets leaving the spraying head have a small electrostatic charge created by electron transfer between the liquid and the walls of the apparatus. We have realised that it is necessary to increase the level of charge on the droplets significantly to enable electrostatic attraction to insects and to other objects to occur, thereby enabling enhanced targeting by the spray and also allowing greater dispersion of the droplets in the air.
Further, we have found that components of the apparatus in contact with the liquid have the ability to influence the charge given to the liquid as it is being sprayed. More particularly it has been found that the charge on the droplets increases with an increase in the contact area between the liquid and the bore-defining portions of the spraying head.